Mechanical Ventilation I
Nazir Habib MD
MVA
Respiration Basics
 Alveoli:Exchange of oxygen and
carbon dioxide
O2
O2
CO2
 Minute ventilation:RR x TV
(normal 7-8 liters)
 BUT Anatomical dead space:
150 mls
 ALVEOLAR Vent 6 liters
CO2
O2
 Normal pH and pCO2
maintained
MVA
Spontaneous Breathing
Exhalation
Inspiration
MVA
Case Study
 48 yr male with diabetes and
pneumonia
 Confused
 Temp 104 , RR 28/min
 ABG 7.32, CO2 38
 Bicarb 16
 pO2 180 on NRB mask
MVA
Indications for
Mechanical Ventilation
Respiratory
muscle fatigue
ALOC :protect airway
Acidosis, sepsis, ALOC, old
Neuromuscular
disease/CNS
DRUGS:Decreased ventilatory drive
Airway obstruction:COPD
Lung Disease: ALI/ARDS
MVA
Indications for
Mechanical Ventilation
 HYPERCAPNIA: fatigue
 HYPOXEMIA: P/Fio2 Ratio? Under
250:why?
 ARDS/ALI or ‘Shunt”
 Deadspace: why
 MISC:
 Cannot protect the airway: Drug overdose, stroke etc.
 Needs a procedure: EGD, TEE, BAL
MVA
Goals of Mechanical Ventilation
 Provide oxygen supplementation
 Assure adequate alveolar minute ventilation
 Reduce work of breathing
 Protect airway from aspiration
 Ensure patient comfort during respiration
 AVOID complications
MVA
Point of Reference:
Spontaneous Ventilation
MVA
Assist-Control Ventilation
 Preset tidal volume OR pressure
 Additional patient-initiated breaths receive preset tidal volume
 Advantages: reduced work of breathing; Rest the muscles
 Disadvantages: hyperventilation
MVA
Volume Ventilation
 Constant flow rate
Pressure
 Guaranteed tidal volume
delivery
 Not affected by lung
impedance
Flow
 Variable pressure
Time
MVA
Pressure-Controlled Ventilation
 Preset airway pressure dialed
 May limit pressure induced lung injury
 Tidal volume may vary with EACH breath: patient
position, resistance/compliance, efforts
 CAUTION!!!!
MVA
Pressure Control Ventilation
 USE with great caution!! TV will vary ……
 Set alarms for high and low TV and minute ventilation
carefully
 AVOID paralysis in this mode
 ASSURE certain TV and VE (VC +, VAPC)
 Consult Critical care
MVA
Synchronized Intermittent Mandatory
Ventilation (SIMV)
Preset
tidal volume at a preset rate
spontaneous breaths rate determined by patient
Often used with pressure support (5-8 cm)
MVA
Synchronized Intermittent Mandatory Ventilation
(SIMV)
 Potential advantages?? Less stacking
 Potential disadvantages
 Higher work of breathing than AC
adequately
Cannot rest patient
 Generally not used
MVA
Pressure-Support Ventilation (PSV)


Pressure assist during spontaneous inspiration
Patient triggered and cycled:
Delivered tidal volume varies: resistance/compliance of lung/thorax

Main use for weaning trials:7-8 cm
MVA
Pressure-Support Ventilation
 Potential advantages
 Patient comfort
 Less WOB than spontaneous breathing
 USE as a weaning mode mostly
MVA
Pressure Ventilation
 Constant insp. pressure
Time Cycled
Pressure
 Decelerating, variable
inspiratory flow rate
 Time cycled: (A)
Flow
Flow Cycled
 Pressure Control
 Flow cycled: (B)
 Pressure Support
MVA
A
B
Continuous Positive Airway Pressure (CPAP)
 No machine breaths delivered
 Spontaneous breathing at elevated baseline
pressure (PEEP)
 Patient controls rate and tidal volume
MVA
Evaluation after Initiation of Mechanical
Ventilation Peak and mean airway pressures
Exhaled
tidal volume and rate
Patient-ventilator synchrony /comfort level
Auto-PEEP
SpO2 and arterial blood gas measurement
Hemodynamic status: BP, HR, sats
MVB 19
®
MVA
Inspiratory Pressures
 Peak inspiratory pressure (Ppeak)
 Inspiratory plateau pressure (Pplat)
Indicator of alveolar distension
Ppeak
Pplat
Pplat
Pplat 30 cm H2O
Inspiration
Ppeak
Expiration
MVA
Inspiratory: Expiratory Ratio
 Determinants of inspiratory time with volume
ventilation
 Tidal volume
 Inspiratory
flow rate
 Inspiratory
waveform
 Inadequate expiratory time
 Incomplete exhalation
 Breath stacking
®
MVA
Auto-PEEP
 Increases peak, plateau, and mean airway
pressures
 Potential harmful physiologic effects:Discuss
 How to detect ..
MVA
Key Points
MVA
Mechanical Ventilation
Monitoring and complications
MVB 24
®
MVA
Case Study: Intubated
 48 yr male with diabetes
and pneumonia, 90 kg , 70
in.
 Confused
 Temp 104 , RR 28/min
 ABG 7.32, CO2 40
 pO2 180 on NRB mask
 Initial settings?
MVA
AVOID Complications Of MV
 Injury to airway from ETT
 Infections: aspiration, VAP
 Lung injury induced by ventilator: VILI..is it ?
 Pressure
 Volume
 Biotrauma
MVA
Monitoring Patients
 Proper monitors ECG, SpO2, vital signs and
capnography essential
 Choose ventilation mode
 Initial FIO2 = 1.0 always
 CHECK ABG then decrease to maintain SpO2 >
92%–94%
 Initial tidal volume = 5-8 mL/kg IBW
MVB 27
®
MVA
Initiation of Mechanical Ventilation
 Set rate and tidal volume ? minute ventilation (target pH, not PaCO2).
 What are the determinants of Minute ventilation?
 ALWAYS check ABGs
 Select PEEP
 Sedate patient !!
 Insert NG tube immediately
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MVA
Respiratory Care Practitioner manage:
• Alarms – Set high and low pressure, low and high tidal
volume and minute volume
• Apnea alarm 20 seconds - 60 sec.
• Flow rate with volume ventilation
• Sputum
• Medications
®
MVA
Oxygenation Evaluate: Hypoxemia
 What is normal ?
 Reason s for HYPOXEMIA : review at this
point
 Correct hypoxemia
 HOW?..............
MVA
®
Ventilation Adequate?: pH or PaCO2
Determine:
Tidal
volume ml/kg IBW
Respiratory rate
Dead space…….normal?
Value
ETCO2 monitor
MVB 31
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MVA
Patient Intubated :Acute Lung Injury / ARDS
 Peak airway pressure (AWP) 52 cm H2O
 Inspiratory plateau pressure (IPP) 48 cm H2O
 RR 20/minute, PEEP 8 cm, TV 600 ml on VC
 Auto-PEEP 0 cm H2O
 SpO2 88%
 pH 7.38, PaCO2 36 torr (4.8 kPa),
PaO2 57 torr (7.6 kPa)
MVA
Next steps…?
 Plateau pressure is HIGH
 Solution?
 Consequence?
 What is your goal..?
 HYPOXEMIA: Why –shunt or deadspace
 How would you know?
 Solutions
 Goal?
MVA
ARDS Management
 Define ARDS and ALI
 Most common causes
 Clinical Manifestations
MVA
CT Scan ARDS
MVA
Ventilation-Induced Lung Injury*
Atelectrauma:
Volutrauma:
Repetitive alveolar collapse and
reopening of the under-recruited
alveoli
Over-distension of normally aerated
alveoli due to excessive volume delivery
*Dreyfuss: J Appl Physiol 1992
MVA
MVA
Barotrauma
MVA
Level 1 Recommendation
MVA
Lung Protective Strategy
1. Set PEEP above the
lower Pflex to keep the
lung open and avoid
alveolar collapse
Volume
2. Apply small Vt to
minimize stretching
forces
3. Set Pplat below the
upper Pflex to avoid
regional overdistension
Pressure
MVA
Trials of Volume- and Pressure-Limited Ventilation Acute
Respiratory Distress Syndrome
Fan, E. et al. JAMA 2005;294:2889-2896.
Copyright restrictions may apply.
MVA
ARDS net strategy
 Adjust TV to 7-5 ml/kg IBW
 Maintain plateau pressure under
30 mm
 Adjust PEEP 8-15 cm to recruit
lung
 Wean FiO2 ASAP
 Lower Mortality (31% vs 40%) NEJM
2000:342:1301
 FLUIDS? Other?
MVA
Putting Things Together
Obstructive Airway Disease
L.W. is a 62-yr-old, 52-kg female
with severe emphysema. For 2
days she has had progressive
dyspnea and was found
unresponsive.
 Required intubation and
initiation of mechanical
ventilation.
MVA
Putting Things Together
Obstructive Airway Disease
ER ventilator settings
 AC rate 14 breaths/min
 FIO2 1.0
 Tidal volume 600 mL
 PEEP 5 cm H2O
 BP is 70/40 mm
 Why..?
MVA
Hypotension after Initiation of Mechanical
Ventilation
 Ventilator: positive intrathoracic pressure
 Decreased venous return, cardiac output,
sedation
 Myocardial ischemia – stress of respiratory
distress, intubation, hypoxemia, acidemia
 Auto-PEEP – effect on intrathoracic pressure
 Hypovolemia
 Tension pneumothorax?
MVB 45
®
MVA
Auto PEEP
 What is Auto-PEEP?
 What situations is it likely to occur?
 How do you detect auto-PEEP?
Clinically
On the ventilator
Decreased expiratory times can
lead to Auto-PEEP
120
.
V
SEC
LPM
1
2
3
Complete exhalation
120
4
5
Incomplete exhalation
causing air-trapping
6
Putting Things Together
Obstructive Lung Disease
Peak
AWP 50 cm H2O, plateau AWP 30 cm H2O;
auto-PEEP
12 cm H2O
Total rate 18 breaths/min
I:E ratio = 1:3
SpO2 100%
pH 7.20, PaCO2 80 torr , PaO2 115 torr
BP

80/60 mm Hg,
heart rate 130–140 beats/min
MVA
Problems
 Hypotension: Why
Solutions
Consequences
 pH is low : resp or metabolic
Solution
Consequences
 Hypoxemia: why –shunt or deadspace
Solution
Consequences
MVA
Permissive Hypercapnia
 Acceptance of an elevated PaCO2, e.g., lower tidal
volume to reduce peak airway pressure
 Contraindicated with increased intracranial pressure
 Consider in severe asthma/COPD and ARDS
 ALLOW low pH..do NOT correct IF risk of injury to
patient
 Discuss with Intensivist advised
MVA
Capnography Depicts Respiration
MVA
Elements of a Waveform
Dead Space
Beginning of
exhalation
Alveolar
Gas
End
of
exhalation
Alveolar gas
mixes with
dead space
Inspiration
MVA
Deadspace?
MVA
SEDATION
 ?Ideal sedative( short acting, causes amnesia and relieves
anxiety)
 Minimal hemodynamic effects
 Is the patient in pain?
 Is the patient at risk of delirium ( old, dementia, alcoholic),
longterm effects? PTSD
 Use protocol driven titration to scale(RASS or Ramsey)
MVA
Sedation: Options
 ALWAYS Use sedation scale eg. Ramsey 1-6 or RASS to titrate
medications
 Versed drip or bolus : fat stores accumulation
 Propofol: short-term, sepsis, BP, Tglyceride?
 Precedex or demametomidine : best?
 Haldol PRN
 Analgesia: Fentanyl, morphine
Refer: SCCM.org guidelines/book
MVA
Neuro-muscular blockers
 AVOID: ULTIMATE chemical restraint!!
 ALWAYS sedate first till asleep
 Check mode and RR set on ventilator
 Check ABG
 List INDICATIONS
 What are the complications
Summary :Ventilator
ARDS/ALI:
 TV 6-8 ml/kg
 RR 20-30/min
 Keep Plateau <30 cm
 PEEP 8-14 cm
 Wean O2
 Fluids /EGDT
Asthma/COPD:
-TV 6-7mls/kg
-RR <14/min
-PEEP low
-Auto PEEP risks
-Give Fluids for BP
-No pressors
-Allow low pH
 Pressors keep MAP >65mm
MVA
Summary
 Evaluate lung pathology: NORMAL vs. Obstructed vs.
ARDS
 UNDERSTAND the physiology!!!
 Hypoxemia? WHY?
 Ventilation:Perfusion matched?
 Evaluate adverse physiological effects:waveforms
 Plateau pressure <30 cm?
MVB 58
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MVA